A conventional electrophotographic image forming apparatus has an image bearing member such as photosensitive drum. The image bearing member supports a toner powder image made through a visualization of an electrostatic latent image by the use of toner particles. The toner powder image is then transferred to a medium such as paper. In this transfer operation, not all the toner particles are transferred onto the medium and a small number of particles stay untransferred on the image bearing member. The untransferred toner particles are then removed from the image bearing member by a cleaning member.
JP 2001-51565 A discloses a cleaning member in the form of blade. As illustrated in FIG. 7, a blade cleaning needs a formation of wedge-like static mass of powder 500 in a triangle zone defined by the surface of the image bearing surface 502 and the blade 504 on the upstream side of the contact region 506 with respect to the moving direction 508 of the image bearing surface 502. The static mass of powder 506, which includes small fragments of toner particles T and additives mixed with or added into the toner, prevents toner particles from moving into the contact region where they can be adhered onto the image bearing surface 502. A part of the mass, i.e., a small amount of toner fragments and additives, flows out of the mass through between the image bearing surface 504 and the opposed blade 502. The loss is compensated by new fragments and additives to be transported by the image bearing surface 504, which results in that the amount of the mass is maintained substantially constant. The amount of toner fragments and additives flowing out of the mass can be controlled by the appropriate selection of the material of the blade 504 and/or adjusting the contact force of the blade 504 against the image bearing surface 502. As discussed above, the mass favorably and effectively prevents the toner particles from passing through the contact region and then scattering into the air which would cause a contamination of the apparatus.
The size of the mass, i.e., the amount of toner fragments and additives forming the mass, can be changed according to the conditions of image formations, for example, the amount of toner particles used for the development of the electrostatic latent image. This results in the change of size of the mass. In particular, the use of toner with less additives and/or the use of smaller toner particles tends to change the size of the mass, which fails to ensure a stable cleaning of the toner particles from the image bearing surface and then causes an unwanted aggregation of the toner particles within the triangle zone which would flow out through the contact region.